Reductive fractionation of larch in a supercritical ethanol medium in the presence of bifunctional Ru/C catalyst and hydrogen donors

Lignin is a bulky waste of the hydrolysis and paper-pulp industry. To solve the problem of its utilization, approaches to deep processing of wood biomass are being developed; they are based on a preliminary catalytic fractionation of wood biomass into main components, which are processed into target products. For the first time, the reductive catalytic fractionation of larch was studied in a supercritical ethanol medium in the presence of 3%Ru/С bifunctional catalyst containing acid groups. The goal of the study was to reveal the effect of the catalyst and features of a hydrogen donor (ethanol, H2, formic acid) on the yields and composition of the products. It was shown that wood hemicelluloses efficiently (ca. 95 wt.%) depolymerize to ethanol at 250 °С. The use of hydrogen in the presence of the catalyst makes it possible to increase the conversion of lignin to 61 wt.% with retaining 47 wt.% cellulose in a solid residue. The maximum conversion of lignin equal to 67 wt.% was obtained in the presence of formic acid; however, the indicated conditions lead to undesirable depolymerization of cellulose (the conversion of 66 wt.%). The main monomeric products of lignin conversion on the catalyst are propenylguaiacol and propylguaiacol. In the liquid products obtained with ethanol and formic acid as the reductants, the content of propenylguaiacol reaches 36 and 33 rel.%, respectively. In the products obtained with hydrogen, the content of propylguaiacol increases to 33 rel.% in the presence of the catalyst.